Method of making superconductors

ABSTRACT

A method of making stabilized superconductors of an intermetallic composition crystallizing according to the A 15 structure, includes the following steps: forming a stock product comprising a core made of the elements of the superconductive composition and a jacket of good heat and electrical conductivity, wiredrawing the stock product to obtain a wiredrawn product in which the jacket is in close engagement with the multielement core and submitting the wiredrawn product to a heat treatment to transform the multielement core into a superconductor.

United States Patent [1 1 Dosdat et a1.

[ METHOD OF MAKING,"

SUPERCONDUCTORS [75] Inventors: Jean Dosdat; Jacques Lanthlez;

Claude Levaire, all of Chauny, France [73] Assignee: Comp agnie F rancaise Thomson Houston-Hotchkiss Brandt, Paris, France [22] Filed: Sept. 13, 1973 [21] Appl. No.: 396,794

Related US. Application Data [63] Continuation of Ser. No. 216,525, Jan. 10. 19 72.

abandoned.

[30] Foreign Application Priority Data Jan. 8. 1971 France r. 71.00518 [52] U.S. Cl 29/599, 174/DIG. 6 [51] Int. Cl H0lv ll/08 [58] Field of Search 29/599; 174/DIG. 6

[56] References Cited UNITED STATES PATENTS 3.218693 11/1965 Allen l74/D1G. 6 X 3.472.944 10/1969 Morton i. 174/DIG. 6 X

[4 1 Mar. 4, 1975 3.548.351 12/1970 Fairbanks 174/D1G. 6 X 3.699.647 10/1972 Bidault 29/599 3,708,606 1/1973 Shattes 174/DlG. 6 X

OTHER PUBLICATIONS Smith Superconducting synchrotrons, in Proceedings of the 1968 Summer Study on Superconducting Devices & Accelerators Part 111 Brookhaven Nat. Lab 6-10, 7-19, 1968, pp. 967-980.

Critchlow et al., Multifilamentary Superconducting Composites in Cryogenics, 2-7], pp. 3-10.

Primary Examiner-E. A. Goldberg Attorney, Agent, or F irm-Edwin E. Greigg 57 ABSTRACT A method of making stabilized superconductors of an intermetallic composition crystallizing according to the A 15 structure, includes the following steps: forming a stock product comprising a core made of the elements of the superconductive composition and a jacket of good heat and electrical conductivity, wiredrawing the stock product to obtain a wiredrawn product in which the jacket is in close engagement with the multielement core and submitting the wiredrawn product to a heat treatment to transform the multielement core into a superconductor.

4 Claims, 4 Drawing Figures This is a continuation of application Ser. No. 216,525, filed Jan. 10, 1972, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to an improved method of making stabilized superconductors as well as to superconductors resulting from such method. The invention is particularly concerned with a method of making stabilizied superconductors of materials which crystallize according to the tungsten B-type structure, that is, an A crystalline structure as designated in the international crystallographic classification.

Superconductors are frequently used in solenoids of the type that are adapted to generate magnetic fields of high intensity. If, by accident. even a small portion of the superconductor momentarily loses its superconductive properties, a larger electric resistance results. As the high intensity current passes through such increased resistance, substantial energy is releasedwith destructive effects. For the purpose of reducing this danger, it has been known to stabilize" the superconductors. Such stabilization consists in juxtapositioning the superconductor to a non-superconductor support of very goodheat and electrical conductivity and to effect a close thermal contact therebetween. In case there is an accidental transition from .a superconductive state to a normal state in one portion of the stabilized superconductor, the, high intensity current in the superconductor is diverted into the support surrounding the superconductor, and as a result, the temperatures generated are usually small. Since the density of the electric current has diminished in the aforenamed portion of the superconductor, this portion is capable to recover more easily its superconductive properties.

Known stabilized superconductors made of intermetallic compositions and crystallizing according to the structure A l5, such as Nb Sn, Nb Al, Nb Au, V Sn, V Ga, Ta Sn, etc. are often expensive or are not capable of providing a good stability of the desired degree. The cause of these disadvantages is to be found mainly in the present methods of manufacturing, particularly those which have not permitted either to economically utilize expensive elements such as niobium, vanadium and tantalum or to provide a uniform stabilizing layer which surrounds the superconductor. Thus, superconductors provided with a stabilizing jacket made of niobium, vanadium or tantalum are often very expensive. On the other hand, there may often be found a malformation of the stabilizing jackets made, for'example, by means of electrolytic deposition. The same disadvantages may be found in superconductors such as Nb Sn, in which the niobium stabilizing jacket is constituted by that part of the niobium body which has not been affected by the diffusion-reaction treatment during the known in-place formation of the intermetallic composition of the superconductor Nb Sn. It is known that the existence or absence of said niobium jacket depends upon the duration and the temperature of the aforenoted diffusion-reaction treatment.

Furthermore, the last-named superconductors are disadvantageous in that they have a substantial anisotropy, a poor stabilization with respect to strong flux fluctuations and further, the conductors cannot be transposed.

OBJECT AND SUMMARY OF INVENTION It is an object of the invention to provide an improved manufacture of stabilized monoor multifil superconductors, particularly those made of a base material that crystallizes accordingto a crystalline structure of A 15 for obtaining stabilized superconductors in an economic manner and without the disadvantages discussed above.

Briefly stated, according to the invention there is provided an improved method which comprises the steps of forming a stock product comprising a core made of coaxially arranged constituent elements of an intermetallic superconductor composition and an external jacket made ofa ductile material having good electrical and thermal conductivity, wiredrawing the stock product to obtain a wiredrawn product in which the jacket is in close engagement with the core and submitting the wiredrawn product to a heat treatment causing an inplace diffusionfreaction of the core elements to transform the latter into an intermetallic superconductive composition.

The invention will be better understood, as well as further objects and advantages will become more apparent, from the ensuing detailed specification of several exemplary embodiments taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FlG.'1 is a fragmentary perspective schematic view of a stock product resulting from a step of the method according to the invention;

FIG. 2 is a fragmentary perspective schematic view of a different stock product resulting from a step of the method according to the invention;

FIG. 3 is a cross-sectional schematic incomplete view of 'a multifilstock product formed of stock products shown in FIGS, 1 or 2 and resulting from a step of the method according to the invention; and

FIG. 4 is a cross-sectional schematic incomplete view of a wiredrawn product resulting from a wiredrawing step performed on the stock product shown in FIG. 3.

DESCRIPTION OF THE EMBODIMENTS As a first step of the method according to the invention for making, for example, a stabilized monofil Nb Sn superconductor, there is formed a stock product comprising a niobium-tin core and a jacket of ductile material having good thermal and electric conductivity. For this purpose, niobium and tin are arranged coaxially with respect to one another and are surrounded by a jacket made, for example, of a material such as copper, nickel, bronze, brass, aluminum, tin alloys, a copper-nickel alloy, non-oxidizable steel or any other material or alloy that may serve as an economic stabilizer for the superconductor.

In the example illustrated in FIG. 1, there is shown a stock product 1 made of a tinned niobium wire core 2 surrounded by a jacket 3 which is formed of a copper tube or a copper sheet rolled into a tube.

In the example shown in FIG. 2, a stock product 4 is formed of a niobium tube 5 (or a niobium sheet rolled into a tube) which is filled with tin or contains a tinwire 6 and a copper jacket 7 formed of a tube or a sheet rolled into a tube and surrounding the core 5, 6.

The stock product 1 or 4 is subsequently submitted, according to the invention, to a wiredrawing step to provide a close contact between the copper jacket and the tin-niobium core and to obtain, as a result of this step, a compact wiredrawn product (not shown) having the desired diameter. The element may subsequently be submitted to an optional rolling operation to transform the same into a compact rolled ribbon.

I The mutual coaxial disposition of the base materials (niobium-tin) in a stabilizing jacket (copper) makes possible to achievea high degree of structural uniformity of the wiredrawn product from which there is obtained, as a result of a thermal treatment to be described hereinafter, a stabilized superconductor having excellent characteristics. By providing, according to the invention, a stabilizing jacket of an economical ductile material (ratherthan niobium, tantalum or the like) which has good electrical and thermal conductivity, the disadvantages discussed in the introductory part of this specification are avoided.

ltvis noted that the method according to the invention may be practiced in the manufacture of any kind of superconductor having a base material of intermetallic composition that, crystallizes according to the crystalline structure A 15, such as Nb Au, Nb Al, Nb AlGe, Nb Sn, Nb Ga, V Ga, V Sn, Ta Au, Ta Sn, etc.

Subsequent to the wiredrawing operation and the optional rolling operation, the'product is submitted to a thermal treatment which is known by itself and which, by a diffusion-reaction process effects an in-place conversion of the core elements into an intermetallic superconductive composition. Dependent upon the na ture ofthe A 15 composition to be formed, the thermal treatment comprises in general a heating ofthe product for a duration of from minutes to 20 hours at a-temperature of 600 -1300 C or, preferably, for a duration of from l0 minutes to hours at a temperature of 800 l(l0() C.

Thus, in the example described hereinabove, the thermal treatment transforms the niobium-tin core into an Nb Sn monofil superconductor.

According to the invention, stabilized multifil superconductors may be made from a stock product as shown in FIGS.,1 and 2. In the manufacture of multifil superconductors of the Nb Sn type, for example, a plu rality of stock products l or 4 or wiredrawn products resulting therefrom are first assembled into a copper jacket 9 to form a multifil stock product 8 as shown in an incomplete manner in FIG. 3. The individual components (stock products or wiredrawn products) may be disposed parallel to the axis of the assembly or may extend helically thereabout to form twisted strands. The multifil stock product 8 is thereafter submitted to a wiredrawing operation to obtain a wiredrawn product 10 (FIG. 4) which is a-compact assembly wherein a close contact exists between each individual jacket 3 or 7 and the niobium-tin core 2 or 5, 6 surrounded thereby and between the individual jackets and the jacket 9. In fact, subsequent to the wiredrawing operation, in the wiredrawn product 10 which has the desired diameter, the individual jackets and the jacket 9 form a homogeneous mass 11 in which the niobium-tin cores are embedded. The wiredrawn product 10 may be subsequently submitted to an optional rolling operation to transform it into a ribbon-like article of desired dimensions (not shown).

Thereafter the wiredrawn product 10, or the ribbonlike article. as the case may be, is submitted to a conventional thermal treatment to effect diffusionwith supports and thereafter be shaped into the desired dimensions. They may also be submitted to transposing operations which consist of giving the axis of the cores a certain inclination with respect to the axis of the finished superconductor. All these operations, however, have to be effected prior to their submission to the thermal diffusion-reaction treatment which transforms the multielement cores into superconductive cores.

According to the invention, the wiredrawn product resulting from the stock product 1, 4 or 8 may be treated thermally to transform it into a superconductor immediately after a wiredrawing or an optional rolling operation.

That which is claimed is:

l. A' method of making astabilized transposed mulcomprising one element of the intermetallic superconductor composition to be obtained, said core being coated with another element of said composition, and a first jacket surroundingsaid core, said first jacket being made of a ductile material having good heat and electric conductivity,

B. wiredrawing said monofil stock product to a desired diameter to obtain a wiredrawn monofil product wherein said jacket is in close engagement with said core,

C. forming a transposed multifil stock product having, as its interior element, a plurality of said wiredrawn monofil products and, as its exterior element, a secondjacket surrounding said interior element, said second jacket being made of ductile material having good heat and electric conductivity,

D. wiredrawing said transposed multifil stock product to a desired diameter to obtain a wiredrawn transposed multiful product wherein said first and second jackets form a homogeneous mass serving as a stabilizing jacket for the transposed multiful superconductor to be obtained and in which the cores are individually embedded, and

E. submitting said wiredrawn transposed multiful product to a heat treatment of a duration of from 5 minutes to 20 hours at a temperature between 600 C and 1300 C to effect an in-place diffusion reaction of the core material for transforming the latter into said intermetallic superconductive composition.

2. A method as defined in claim 1 wherein the materials of said cores are selected from elements of the intermetallic superconductive composition group consisting of Nb Sn,' Nb Au, Nb Al, Nb AlGe, Nb Ga, V Sn, V Ga, Ta Sn, Ta Au, Ta Al, Ta Ga.

3. A method as defined in claim 1, wherein the material of said first and second jackets is selected from the group consisting of copper, nickel, aluminum, bronze, brass, copper-nickel alloy and non-oxidizable steel.

4 A method as defined in claim 1, wherein said first jacket is made of a material identical to that of said second jacket. 

1. A method of making a stabilized transposed multifil superconductor made of an intermetallic superconductor composition crystallizing according to the crystalline structure A 15, comprising the following steps: A. forming a monofil stock product having a core comprising one element of the intermetallic superconductor composition to be obtained, said core being coated with another element of said composition, and a first jacket surrounding said core, said first jacket being made of a ductile material having good heat and electric conductivity, B. wiredrawing said monofil stock product to a desired diameter to obtain a wiredrawn monofil product wherein said jacket is in close engagement with said core, C. forming a transposed multifil stock product having, as its interior element, a plurality of said wiredrawn monofil products and, as its exterior element, a second jacket surrounding said interior element, said second jacket being made of ductile material having good heat and electric conductivity, D. wiredrawing said transposed multifil stock product to a desired diameter to obtain a wiredrawn transposed multiful product wherein said first and second jackets form a homogeneous mass serving as a stabilizing jacket for the transposed multiful superconductor to be obtained and in which the cores are individually embedded, and E. submitting said wiredrawn transposed multiful product to a heat treatment of a duration of from 5 minutes to 20 hours at a temperature between 600* C and 1300* C to effect an in-place diffusion reaction of the core material for transforming the latter into said intermetallic superconductive composition.
 2. A method as defined in claim 1 wherein the materials of said cores are selected from elements of the intermetallic superconductive composition group consisting of Nb3Sn, Nb3Au, Nb3Al, Nb3AlGe, Nb3Ga, V3Sn, V3Ga, Ta3Sn, Ta3Au, Ta3Al, Ta3Ga.
 3. A method as defined in claim 1, wherein the material of said first and second jackets is selected from the group consisting of copper, nickel, aluminum, bronze, brass, copper-nickel alloy and non-oxidizable steel.
 4. A method as defined in claim 1, wherein said first jacket is made of a material identical to that of said second jacket. 